In modern motor cars, there is an increasingly widespread presence of active and passive safety devices. In particular, inserted within the passenger compartment of a motor car is an increasing number of airbags in an attempt to protect all the occupants of the motor car in the best possible way in the event of an accident.
There is by now present in almost all new motor cars a front airbag for the passenger, said airbag being set in a housing within the dashboard that is closed at the front by a lid. In currently produced cars, there exist two types of lid for the airbag: either in view, i.e., visible on the aesthetic part of the trim, or else hidden from view, i.e., integrated in the skeleton and not visible on the aesthetic part of the trim.
In motor cars with the lid integrated in the skeleton, the coating material of the trim can be made of fabric, leather, or plastic material. To enable opening of the lid of the airbag in the event of an accident, at a point corresponding to the lid itself, the coating layer is pre-weakened by means of an internal line of incision (and hence not visible from the passenger compartment) that runs along the perimeter of the lid.
In known applications, the trim supporting the lid of the airbag has an inner layer made of moulded plastic material of a thermoplastic type (for example, polypropylene) that constitutes the skeleton, an intermediate layer made of spongy plastic material that bestows softness to the touch, and an outer coating layer having aesthetic purposes (for example, made of fabric or leather). However, providing the inner layer made of moulded plastic material of a thermoplastic type involves the construction of a relatively complex and costly production plant that calls for a yearly output of at least a few hundreds of thousands of pieces in order to be economically advantageous. Consequently, the use of moulded plastic material of a thermoplastic type may not be economically sustainable for a limited yearly output (for example, fewer than 4000-5000 pieces per year).
For a limited yearly production, it is economically advantageous to make the inner layer of the trim supporting the lid of the airbag made of thermosetting plastic material; however, thermosetting plastic materials are generally less elastic and more brittle than thermoplastic plastic materials. Consequently, using a thermosetting plastic material for making the inner layer of the trim supporting the lid of the airbag may give rise to the risk, at the moment of inflation of the airbag, of the lid bursting into pieces, with the slivers projecting (at least partially) in the direction of the passenger and thus constituting a serious hazard.
Furthermore, U.S. Pat. No. 6,092,835A1, which is incorporated by reference, discloses an automotive instrument panel having a concealed airbag. A molded substrate having first and second surfaces and an aperture there through receives an airbag; a curved metal door is secured to the second surface of the substrate by a plurality of fasteners extending through the substrate. The metal door has a generally U-shaped slot with first and second ends being spaced apart a distance greater than the length of the aperture. A molded covering overlies the second surface and the door and is secured thereto with an intermediate layer of foam and a foam gasket overlies the slot between the door and the substrate; a foam impermeable layer is placed between the gasket and door to prevent injected foam from impregnating the foam gasket and interfering with the opening of the door.